wip(assembler): round L12 -- region pages keep LOD1 block proofs: 24 m crossing 5x faster

Analytic region pages now retain the immutable shared manifest, so LOD1 page tiles get the L9
uniform-block proofs (71.7 -> 5.6 ms per tile). Reviewer W12 no-hash: 24 m crossing 0.898 ->
0.166 s; Luna: 1 km 5.89 -> 1.25 s. Spawn unchanged; all L1/FloatingIslands hashes and the 24 m
crossing hash unchanged (W1/W12).
KNOWN BUG (pre-existing, measured here): the same tile key yields different density from the base
shape (manifest field) than from a region page (legacy field), sometimes different mesh too, so
output depends on streaming history. To be fixed in L13.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CSFYgsdW8ejZSyiMf4qRSX

Standalone/Source/StreamBenchmarkHeadless.cpp

@@ -42,6 +42,7 @@ namespace
         bool ScreenSpaceGate=false;
         bool AuditUniformBlockProofs=false;
         bool ProfileLodWork=false;
+        bool AuditBasePageEquivalence=false;
         bool RegionCrossing=false;
         bool AuditTileShapeReadiness=false;
         int DiagnosticSlowShapeCompileMs=0;
@@ -120,6 +121,7 @@ namespace
                     "  --screen-space-gate (measure display error and historical negative controls)\n"
                     "  --audit-uniform-block-proofs (fill and check every interval-certified block)\n"
                     "  --profile-lod-work (report per-LOD density sample counts)\n"
+                    "  --audit-base-page-equivalence (hash one tile through both shape routes)\n"
                     "  --audit-tile-shape-readiness (run a deliberately mis-marked tile against the native-only guard)\n"
                     "  --diagnostic-slow-shape-compile-ms=N (diagnostic overlap control; default 0)\n"
                     "  --render-distance-chunks=N (0 disables the extra far ring)\n"
@@ -139,6 +141,7 @@ namespace
             else if(arg=="--screen-space-gate")options.ScreenSpaceGate=true;
             else if(arg=="--audit-uniform-block-proofs")options.AuditUniformBlockProofs=true;
             else if(arg=="--profile-lod-work")options.ProfileLodWork=true;
+            else if(arg=="--audit-base-page-equivalence")options.AuditBasePageEquivalence=true;
             else if(arg=="--region-crossing")options.RegionCrossing=true;
             else if(arg=="--audit-tile-shape-readiness")options.AuditTileShapeReadiness=true;
             else if(arg=="--auto-surface-camera")options.AutoSurfaceCamera=true;
@@ -370,5 +373,5 @@ int main(int argc,char** argv)
         options.CameraPitchDegrees,options.ScreenSpaceGate,options.UseSharedColumnCache,
         cameraStepVoxels,options.AuditUniformBlockProofs,options.ProfileLodWork,
         options.RegionCrossing,options.AuditTileShapeReadiness,
-        options.DiagnosticSlowShapeCompileMs);
+        options.DiagnosticSlowShapeCompileMs,options.AuditBasePageEquivalence);
 }